A little thought of before the Big Bang

[Peter Watkins]

Hello Marcus. RE #22. Is the universe that you are picturing, our universe or the one that may have existed, and collapsed, before ours? Your description, a 3d sphere of changing circumference, is how I picture our universe. The only difference is that I think that the increased rate of galaxy separation is caused by a slowing rate of expansion. However, that's by the by.
You say that it is thought that at high densities, gravity reverses and repels. So how come there are massive black holes at the centre of all galaxies? Density cannot be greater than within a black hole, be it large or small.
There is of course an eternal universe. It is the wider universe from whence we came!

 

[Chalnoth]

Hello Marcus. RE #22. Is the universe that you are picturing, our universe or the one that may have existed, and collapsed, before ours? Your description, a 3d sphere of changing circumference, is how I picture our universe. The only difference is that I think that the increased rate of galaxy separation is caused by a slowing rate of expansion. However, that's by the by.

It's also wrong. The rate of galaxy separation would only increase faster if the expansion rate (the Hubble parameter) was increasing. The expansion rate appears today to be asymptotically approaching a constant value (this is what it would do in the presence of a cosmological constant). At a constant expansion rate, the galaxy separation will still accelerate.

I'd like to mention, by the way, that I tend to expect that the overall geometry of our universe is highly, highly unlikely to be anything so simple and symmetric as a sphere. More likely it is some very irregular shape, perhaps with any number of twists and loops in higher dimensions. It's possible that it has the topology of a sphere, of course, but it's unlikely that it has the shape of one.

You say that it is thought that at high densities, gravity reverses and repels. So how come there are massive black holes at the centre of all galaxies? Density cannot be greater than within a black hole, be it large or small.

That just says that an expanding universe would, from the outside, look like a black hole. Just because it looks like a black hole from the outside doesn't mean there aren't interesting things going on inside, however.

There is of course an eternal universe. It is the wider universe from whence we came!

Possible, but not certain.

 

[apeiron]

I'd like to mention, by the way, that I tend to expect that the overall geometry of our universe is highly, highly unlikely to be anything so simple and symmetric as a sphere. More likely it is some very irregular shape, perhaps with any number of twists and loops in higher dimensions. It's possible that it has the topology of a sphere, of course, but it's unlikely that it has the shape of one.

.

What are the reasons for thinking this? If the curvature looks so flat to us, does this not imply that all irregularities will have been stretched smooth and so a simple hypersphere is the most probable story? What's your line of thought here?

 

[Chalnoth]

What are the reasons for thinking this? If the curvature looks so flat to us, does this not imply that all irregularities will have been stretched smooth and so a simple hypersphere is the most probable story? What's your line of thought here?

There are two main considerations here.

1. Inflation ensures that no matter how complicated or ugly the shape of the universe as a whole is, it still looks flat to any observers that appear from an inflated region.

2. Even if it started off as a hypersphere, different phase transitions in the early universe would have occurred differently in different locations, causing different expansion rates, which would cause the overall shape to diverge significantly from a perfect sphere.

 

[apeiron]

There are two main considerations here.

1. Inflation ensures that no matter how complicated or ugly the shape of the universe as a whole is, it still looks flat to any observers that appear from an inflated region.

2. Even if it started off as a hypersphere, different phase transitions in the early universe would have occurred differently in different locations, causing different expansion rates, which would cause the overall shape to diverge significantly from a perfect sphere.

Right, so the assumption is of Linde style inflation with multiple local coolings and phase transitions into expanding universe-lets? And you are speaking of the shape of the whole?

Or this is a domain type argument. One single inflation event with multiple regions crystalising out with different local organisations around the same time?

If this is Lindean, then is natural to think of such a pre-bang realm as either flat and infinite in extent, or closed and connected? The other two options would seem to be fractal or locally hyperbolic.

 

[Chalnoth]

Right, so the assumption is of Linde style inflation with multiple local coolings and phase transitions into expanding universe-lets? And you are speaking of the shape of the whole?

Or this is a domain type argument. One single inflation event with multiple regions crystalising out with different local organisations around the same time?

If this is Lindean, then is natural to think of such a pre-bang realm as either flat and infinite in extent, or closed and connected? The other two options would seem to be fractal or locally hyperbolic.

My argument is vastly more basic than this, and isn't dependent upon a particular model of inflation. Point one is just based upon the general feature of inflation where any amount or sort of curvature is driven asymptotically flat due to the expansion. This doesn't mean that the universe becomes actually flat, just that the universe becomes so large that the curvature becomes unnoticeable.

Point two is just based upon another general feature of the universe where it appears that spontaneous symmetry breaking events appear to be part of our past, which would indicate that they happened differently elsewhere.

 

[Peter Watkins]

Re #32. Why would an expanding universe look, from the outside, like a black hole, and what has this to do with black holes at the centre of galaxies not being blown asunder by reversed gravity?
With regard to universal geometry, you are quite right. The means by which our universe came into being would have produced a very untidy shape, the uniform sphere would be for illustrative purposes only, much as a straightened line of galaxies can be used to illustrate both the red-shift conundrum and how gravitational drag can cause galaxies to move apart at ever increasing rates.

 

[Chalnoth]

Re #32. Why would an expanding universe look, from the outside, like a black hole, and what has this to do with black holes at the centre of galaxies not being blown asunder by reversed gravity?

Unfortunately I don't remember the argument right now as to why a region like our own would look like a black hole from the outside (it can't help that I'm a bit tired now...), but the answer to why black holes aren't blown apart is pretty simple: they're surrounded by an event horizon. All manner of interesting things could be happening in the interior of a black hole, but all that happens in there is forever hidden from our universe due to this event horizon.

 

[apeiron]

The means by which our universe came into being would have produced a very untidy shape, .

Ah, again the question is what is the quantitative model of this "untidyness". Are we talking a gaussian or powerlaw messiness? To me, one reduces to the simplicity of the closed hypersphere, the other is an open fractal.

 

[Peter Watkins]

But presumably the fact that the event horizon that surrounds a black hole is still intact states that the black hole is not, and has not been, being broken apart by the reversal of gravity.

 

[marcus]

But presumably the fact that the event horizon that surrounds a black hole is still intact states that the black hole is not, and has not been, being broken apart by the reversal of gravity.

The re-expansion would not affect how things look in this region. The re-expansion forms a new expanding region of space which does not intersect with ours.

There have been paper after paper on this, during the past 3 years or so. Many computer simulations, also analytic solutions. The direction of research is to extend the results to more and more realistic models, by getting rid of simplifying assumptions, like symmetry.

The first work was done with symmetric models, looking the same in all directions (which means there is less to calculate---either the equations to be solved are simpler or the computer program is simpler.) Now less symmetric cases have been studied.

The effect of the reversal is to cause a re-expansion "out the bottom" so to speak. In fact already in the classical black hole picture, time and causality point down the hole, once you are inside the horizon. So once you pass the classical horizon, time is already pointing in the right direction.
In the classical model, time-evolution stops when you hit the failure-point---a "singularity" is where the classical theory stops functioning and no longer gives valid results, typically some number blows up.

The difference with the quantized theory is that it doesn't blow up or fail---time keeps on going, very high density is reached and the contracting geometry re-expands to form a new region.

However the quantized theories have to be tested. And they differ as to details. They are not to believe in, just something to know about which clever people will have to devise some means to test observationally.

 

[ViewsofMars]

The Big Bang
The night sky presents the viewer with a picture of a calm and unchanging Universe. So the 1929 discovery by Edwin Hubble that the Universe is in fact expanding at enormous speed was revolutionary. Hubble noted that galaxies outside our own Milky Way were all moving away from us, each at a speed proportional to its distance from us. He quickly realized what this meant that there must have been an instant in time (now known to be about 14 billion years ago) when the entire Universe was contained in a single point in space. The Universe must have been born in this single violent event which came to be known as the "Big Bang."
http://nasascience.nasa.gov/astrophysics/focus_area_list

Oh, and don't forget to read ...

Wilkinson Microwave Anisotropy Probe. I love it!
http://map.gsfc.nasa.gov/

I encourage everyone to read the pdf below from NASA, Wilkinson Microwave Anisotropy Probe . Here's a snippet from it.

Please avoid the following common misconceptions about the Big Bang and expansion:

-The Big Bang did not occur at a single point in space as an "explosion." It is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite. If it is closed and finite, then it was born with zero volume and grew from that. In neither case is there a "center of expansion" - a point from which the universe is expanding away from. In the ball analogy, the radius of the ball grows as the universe expands, but all points on the surface of the ball (the universe) recede from each other in an identical fashion. The interior of the ball should not be regarded as part of the universe in this analogy.

-By definition, the universe encompasses all of space and time as we know it, so it is beyond the realm of the Big Bang model to postulate what the universe is expanding into. In either the open or closed universe, the only "edge" to space-time occurs at the Big Bang (and perhaps its counterpart the Big Crunch), so it is not logically necessary (or sensible) to consider this
question.

-It is beyond the realm of the Big Bang Model to say what gave rise to the Big Bang. There are a number of speculative theories about this topic, but none of them make realistically testable predictions as of yet. To this point, the only assumption we have made about the universe is that its matter is distributed homogeneously and isotropically on large scales. There are a number of free parameters in this family of Big Bang models that must be fixed by observations of our universe. The most important ones are: the geometry of the universe (open, flat or closed); the present expansion rate (the Hubble constant); the overall course of expansion, past and future, which is determined by the fractional density of the different types of matter in the universe. Note that the present age of the universe follows from the expansion history and present expansion rate.
http://map.gsfc.nasa.gov/universe/WMAP_Universe.pdf

I've left a little bit of me on each page now.

 

[Peter Watkins]

So spontaneous creation, which is but a short step from divine creation, is now the official view? I always thought that these were the refuge of those who couldn't be bothered to figure it out.

 

[Chalnoth]

So spontaneous creation, which is but a short step from divine creation, is now the official view? I always thought that these were the refuge of those who couldn't be bothered to figure it out.

Well, saying that our universe was born in the big bang is certainly not the same as declaring spontaneous creation. It is definitely the case that our universe had to have some type of beginning. The question is what kind of beginning that was, and how it came about. We don't know yet, but we're working on it.

 

[marcus]

So spontaneous creation, which is but a short step from divine creation, is now the official view?...

Are you kidding, Peter? The standard (now rather old) BB Model does not cover the very beginning---says nothing about it. There are newer models that do, but they have as yet not been confirmed by testing.

That doesn't imply any claim that there was a "spontaneous creation" or an abrupt beginning of temporal evolution.

Have a look at "A Tale of Two Big Bangs" at the Einstein Institute public outreach website called Einstein Online. The link is in my sig.

It is probably less dumbed down than the NASA stuff that Mars cited.

 

[Chronos]

Peter, you seem fixated on the idea the universe is a gigantic black hole [as viewed by 'God']. Current observational evidence does not support that hypothesis. Do you have evidence in mind that affirms your idea?

 

[Chalnoth]

Peter, you seem fixated on the idea the universe is a gigantic black hole [as viewed by 'God']. Current observational evidence does not support that hypothesis. Do you have evidence in mind that affirms your idea?

Compute the Schwarzschild radius of the mass in the visible universe (out to the surface of last scattering).

 

[Chronos]

That would be amazing, if it worked. It doesn't.

 

[Chalnoth]

That would be amazing, if it worked. It doesn't.

In what way doesn't it work?

 

[ViewsofMars]

August 13, 2009

PLANCK SEES LIGHT BILLIONS OF YEARS OLD

A full-sky map of simulated cosmic microwave background (CMB) data. Image credit: ESA [Look at the image on-line by clicking the last link within this quote.]

The Planck space telescope has begun to collect light left over from the Big Bang explosion that created our universe. The mission, which is led by the European Space Agency with important participation from NASA, will help answer the most fundamental of questions: How did space itself pop into existence and expand to become the universe we live in today? The answer is hidden in ancient light, called the cosmic microwave background, which has traveled more than 13 billion years to reach us. Planck will measure tiny variations in this light with the best precision to date.

The mission officially started collecting science data today, Aug. 13, as part of a test period. If all goes as planned, these observations will be the first of 15 or more months of data gathered from two full-sky scans. Science results are expected in about three years.

Read about NASA and JPL's role in the mission at http://www.nasa.gov/mission_pages/planck/overview.html.
More information about the mission is also online at http://www.esa.int/SPECIALS/Planck/index.html.
###

http://planck.caltech.edu/news20090813.html

Please stay tuned-in for upcoming results. What a wonderful time to be living in. I love it! Thank you, George F Smoot from Lawrence Berkeley National Laboratory for your article in CERN Courier, Jun 8, 2009 that alerted me of this discovery as noted above. You are fantastic! One of the best of the best.http://cerncourier.com/cws/article/cern/39163)

(I've now contributed on 4 pages to this topic.)

 

[Peter Watkins]

Quite how Chronos figured that I view the universe as a giant black hole is difficult to imagine. It is a flight of fancy that exceeds even that of dark energy and expanding space.
With regard to the reversal of gravity at extreme densities, how would that work? Surely, once the reversed gravity caused a degree or so of expansion, density would decrease, gravity would revert and collapse would commence once again, leading to renewed expansion, and so on, an infinitum. All within tiny time cycles I assume. It doesn't sound like a realistic proposal for the bringing into being of our little universe.

 

[Chalnoth]

With regard to the reversal of gravity at extreme densities, how would that work? Surely, once the reversed gravity caused a degree or so of expansion, density would decrease, gravity would revert and collapse would commence once again, leading to renewed expansion, and so on, an infinitum. All within tiny time cycles I assume. It doesn't sound like a realistic proposal for the bringing into being of our little universe.

Well, I really don't know, but here's one scenario under which you might get a sort of bounce:

Imagine, for a moment, that if matter is condensed to extraordinary amounts (as you'd get near the center of a black hole), that it tends to start to transfer its energy into a sort of a scalar field that acts like an inflaton, and you end up with a small region of space that has an exceedingly high energy density spread relatively evenly across said region. If matter tends to approach this configuration at the highest of densities, then it would tend to produce an inflating region of space. Now, because of the geometry, there's no way this inflating region could expand into the surrounding space, but would instead produce new space within its own region, sort of expanding "out the bottom" of the black hole.

This is just a pie-in-the-sky idea, though. I have no idea if the actual bounce ideas are like this, or if it's remotely likely. But it's one on-the-surface plausible way in which you might get a sort of "bounce".

 

[Chalnoth]

By the way, I'd like to add on a little bit of an explanation for my previous reply to Chronos on our universe being a black hole when viewed from the outside:

First, the limit to which we can see with visible light is the surface of last scattering. We know that our universe extends beyond this for quite some ways, but that's okay for this calculation. The idea is pretty simple: let's imagine, just for kicks, that our universe ends just beyond the CMB (this isn't really possible, but it serves as a fair thought experiment). Beyond that, there is nothing but empty space (and dark energy).

In this little thought experiment, that would make our universe a spherically-symmetric universe with a given mass. I compute the average normal/dark matter density of the universe, from the WMAP 5-year best-fit parameters, as being:
\rho_m = 2.49 \times 10^{-24} \mathrm{gm/m^3}

Given this, the total mass of our universe out to the surface of last scattering is:
m = 8.91 \times 10^{56} ~\mathrm{gm}

That's a fairly big number. But what's the Schwarzschild radius for a mass this large? Well:
r_s = \frac{2Gm}{c^2} = 42,900 ~\mathrm{Mpc}

Compare that to the distance to the surface of last scattering:
d_A = 14,279 \mathrm{Mpc}

Now, given the nature of Gauss's Law, it seems to me that this means that if our universe suddenly ends just past the limits of our vision, then the collective gravity of everything in our visible universe makes it so that when viewed from outside, our universe would look like a black hole (since it'd be surrounded by an event horizon with area given by the radius 42,900 Mpc).

But what if we step back a moment, and recognize that our universe doesn't end just beyond the limits of our vision? This is pretty much necessarily the case, as we don't expect an abrupt end to our universe, but instead some sort of tapering off or some such. In that situation, then we have to examine how the Schwarzschild radius r_s scales with increased size.

That's pretty easy to do. Just consider that the Schwarzschild radius r_s is linear with mass, but mass increases as the cube of the radius of the universe. This means that if the universe extends beyond the limits of our vision, then the Schwarzschild radius gets even larger.

Therefore it definitely appears to me that our universe, if it has any boundary, must have an event horizon outside of that boundary, hiding it our region of space-time from communicating with any other: we would look like a black hole to anybody "outside" our universe.